var ajax = false;
var READY_STATE_UNINITIALIZED = 0;
var READY_STATE_LOADING       = 1;
var READY_STATE_LOADED        = 2;
var READY_STATE_INTERACTIVE   = 3;
var READY_STATE_COMPLETE      = 4;
// AjaxCall('news.php', 'newsid=5', 'GET', 'alertContents')
function AjaxCall(url, params, httpMethod, callBack) {
    httpMethod = (httpMethod == 'POST')? 'POST' : 'GET';
    ajax = false;

    if (!params) {
        params = null;
    }

    // Asyncronous Javascript And XML (AJAX)
    // create the XMLHttp object (Cross-Browsers)
    if (window.XMLHttpRequest) {       // Mozilla, Safari,...
        ajax = new XMLHttpRequest();
        if (ajax.overrideMimeType ) {
            ajax.overrideMimeType('text/xml');
        }
    } else if (window.ActiveXObject) { // Internet Explorer
        try {
            ajax = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                ajax = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {}
        }
    }

    // unable to create XMLHTTP objects
    if (!ajax) {
        alert('Giving up :( Cannot create an XMLHTTP instance');
        return false;
    }

    if (httpMethod == 'GET') {
        url = url + '?' + params;
    }

    ajax.onreadystatechange = eval(callBack);
    ajax.open(httpMethod, url, true);

    if (httpMethod == 'POST') {
        ajax.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    }
    ajax.send (params);
}
/*
<div id="loadingBox" style="display:none">Loading ...</div>
<div id="contentBody">
Ahlan
</div>
*/
function alertContents() {
    if (ajax.readyState != READY_STATE_COMPLETE) {
        document.getElementById('loadingBox').top = screen.availHieght / 2;
        document.getElementById('loadingBox').left = screen.availWidth / 2;
        document.getElementById('loadingBox').style.display = '';
        document.getElementById('contentBody').innerHTML = '';
    }
    if ( ajax.readyState == READY_STATE_COMPLETE) {
        document.getElementById('loadingBox').style.display = 'none';
        if (ajax.status == 200) {
            document.getElementById('contentBody').innerHTML = ajax.responseText;
            document.getElementById ('contentBody').style.display = '';
        } else {
            alert('There was a problem with the request. Error: ' + ajax.status);
        }
    }
}